Supported features

pyxsd 1.0 implements a substantial, honest subset of XSD 1.0. This page summarizes what is validated, with pointers to the regression corpus that backing every claim (66 independently authored manifest-driven cases inspired by the W3C XMLSchema1TestSuite and NIST datatype feature areas — run uv run python tests/report_conformance.py for the live pass-rate report).

Built-in type lattice

All 45 XSD 1.0 built-in simple types are implemented with lexical validation in __new__ (pyxsd.xsd_data_types): the full string family (string, normalizedString, token, Name, NCName, NMTOKEN, language, ID, IDREF, ENTITY, anyURI, QName), all integer variants with correct ranges, decimal, float/double (including INF/-INF/NaN), the date/time family (date, dateTime, time, duration, gYear, gYearMonth, gMonth, gMonthDay, gDay), base64Binary, hexBinary, anySimpleType/anyType, and the list types NMTOKENS/IDREFS/ENTITIES.

Structural schema elements

• xs:sequence, xs:choice, xs:all content models with order and occurrence checking

• xs:group definitions and references (nested, with occurrence folding and cycle detection)

• xs:attributeGroup definitions and references

• xs:any / xs:anyAttribute wildcards with namespace lists (##any, ##other, ##local, ##targetNamespace, explicit URIs) and processContents (strict / lax / skip), enforced in namespaced mode

• XML Namespaces in namespaced mode: targetNamespace, elementFormDefault / attributeFormDefault, prefixed type/ref QNames, cross-namespace xs:import, and QName value identity

• xs:union (declared members and inline anonymous members)

• element references (ref) and substitution groups

• complex content xs:extension / xs:restriction derivation with final enforcement

Instance semantics

• minOccurs/maxOccurs enforcement (including unbounded)

• xsi:nil on nillable elements (nil instances preserved in output)

• default and fixed for attributes and simple-content elements

• xsi:type dynamic dispatch on child elements and the document root

• abstract elements and types; block/prohibited restrictions

• root dispatch: both complex-typed and primitive-typed document roots

• expanded-name matching of elements and attributes against form defaults (namespaced mode)

Composition and identity

• xs:include (chameleon schemas supported), xs:import (cross-namespace components in namespaced mode, including imports without a schemaLocation when the namespace is supplied), xs:redefine (single level)

• xs:key, xs:unique, xs:keyref with an XPath subset (child steps, .// descendants, *, ., @attr, multi-step paths)

Validation reporting

Non-fatal, code-tagged issue reporting via PyXSD.report (see Validation), plus --strict CI-friendly exit codes and the ValidationReport API for library users. PyXSD(mode=...) / --mode selects how invalid or unrecognized content is bound (strict vs. lax) without changing what is reported — see Parse modes and binding. The same policy carries a namespaces field: PyXSD(mode=ParseModes.NAMESPACED) or --namespaces strict turns on namespace-aware validation (the default legacy behavior is unchanged).

Known gaps

Feature	Construct	Status	Note
Namespace-aware schemas	targetNamespace, elementFormDefault=qualified	partial	Opt-in in namespaced mode (ParseModes.NAMESPACED / --namespaces strict); the default legacy mode keeps local-name matching. Namespace-qualified identity-constraint selectors and reporting an unbound prefix in an instance QName value are not implemented.
Facets on user simpleTypes	enumeration, pattern, length, …	ignored	Every built-in type’s own lexical rules and whitespace mode are enforced, but facets declared on user-defined simpleTypes are not. xs:QName lexical form is checked; prefixes resolve against the instance context in namespaced mode.
Wildcard namespace filtering	processContents, namespace lists	partial	Enforced in namespaced mode (including wildcard-no-declaration under strict); legacy mode passes undeclared content through permissively.
Full identity XPath	xs:selector/xs:field expressions	partial	Predicates, absolute paths, positional steps, and other axes are skipped with a warning.
List type derivation	xs:list user types	unsupported	Built-in list types work; user-defined list types are not generated.
Unions of list members	xs:union with list members	partial	Unions of atomic types work (including inline anonymous members).
Mixed content	mixed="true"	ignored	Interleaved text is not preserved or validated.
Remote schema hints	URL schemaLocation	partial	Local file system resolution only.
Notation	xs:NOTATION	unsupported	Not implemented.
Redefine chains	redefining an already-redefined component	partial	A single redefine level is supported.
Unique particle attribution	UPA checking	ignored	Content models are matched greedily in document order.

This table is maintained as machine-readable data in tests/conformance/unsupported.toml, which also feeds the conformance report.